Long-Term Fertilization on Sustenance of High-Production Farming in an Inceptisol.
Malarvizhi Palaniappa pillai, Selvi Duaisamy, and Gopalakrishnan Mylesamy. Professor, Dept of SS&AC, Tamil Nadu Agricultural Univ, Lawley Road, Coimbatore-641 003, India
Field experiments with fixed crop rotation of finger millet - maize - cowpea sequence were conducted in the on-going All India Co-ordinated Research Project on Long Term Fertilizer Experiment at Tamil Nadu Agricultural University farm, Coimbatore since 1972. The treatments are: T1:50% NPK; T2:100% NPK (optimal); T3:150% NPK; T4:100% NPK with hand weeding, T5:100% NPK + ZnSO4 (maize); T6:100% NP; T7:100% N alone; T8:100% NPK+FYM (finger millet); T9:100% NPK (S free) and T10:Control. The trend in crop yields over the years from 1972 to 2004 indicated that the crop yields of finger millet, maize, grain and fodder cowpea were continuously lower under control and nitrogen alone treatments and higher under 100% NPK+FYM treatments suggesting that in absence of farmyard manure, the soil productivity declines suggesting the need for balanced fertilization for improving soil fertility and crop productivity. The overall pooled 32 years of crop productivity depict that the treatments effect on productivity was in the order of 100 % NPK + FYM >150 % NPK > 100%NPK + Zn > 100 % NPK >100 % NPK ( S free) > 100 % NPK + HW > 100% NP > 50 % NPK > 100 % N > control. There was no additional response to the application of K (NPK) over that of N and P alone on the grain yield of maize. Omission of inorganic nutrients (control) could not sustain high productivity of crops as that of 100 % NPK. Continuous application of nitrogenous fertilizers alone adversely affected the crop productivity resulting in drastic reduction of yield to an extent of 75 - 80% in finger millet, maize and cowpea. Hence, farmers are cautioned from indiscriminate use of nitrogenous fertilizers alone which will not only deteriorate the soil health and also the crop productivity. Exclusion of P from the fertilizer schedule resulted in drastic reduction of available P which led to the improper root development, leading to deleterious effects on growth and yield. There was no response to applied K; this could be attributed to the fact that these soils are rich in potassium and continuous release of appreciable amounts of K from the soil reserve has occurred resulting in a shift in the equilibrium besides addition of appreciable quantities of K through irrigation water (15 mg L-1). Continuous exclusion of S from the fertilizer schedule had no adverse effect on the yields of finger millet, maize and cowpea crops but there was a yield reduction in the recent years. This might be due to the gypsiferous nature of the soil with fair amounts of sulphur and appreciable quantities of sulphur being added through irrigation water (35 mg L-1). Graded levels of NPK fertilization from 50 per cent to 150 % NPK substantially enhanced the removal of NPK from soil by all the crops. Keeping 100 per cent NPK as optimum dose, the removal of NPK per ton of crop produce was 35.12, 5.42 and 39.80 kg t-1 by finger millet and 28.17, 3.28 and 38.83 kg t -1 by maize and 113.85, 16.08 and 78.16 kgt-1 by grain cowpea respectively. However, the continuous integration of 100 % NPK + 10 t FYM ha-1 maximized the productivity of all crops in the cropping sequence, while the least removal was with 100 per cent N alone and control. On an average to produce one tonne of finger millet + one tonne of maize, the total nutrient removal was 63.29, 8.70 and 78.63 kg N, P, K respectively. The nutrient uptake in unfertilized cropped plot was low which might be due to lower dry matter yield and nutrient content of the crops. Key words: Long term fertilization, yield sustenance, nutrient removal, intensive cropping.